Line traps for power line carrier current systems

ABSTRACT

A line trap is provided in an arrangement facilitating current balance between a plurality of layers as well as providing mechanical stability. The line trap includes a coil of an electrical conductor with an end frame at each end that comprises a plurality of bars extending radially outward from a central hub. The radial bars are mechanically attached to the coil structure and also provide a path for electrical conduction from the layers of the coil to centrally located connector taps. The radial bars also permit terminating coil layers at desired fractions of a turn to achieve current balance. Preferably the layers of the coil have turns uniformly spaced from the axis with uniform spacing between adjacent turns of all the layers.

United States Patent [is] 3,696,315 Riggins [4 Oct. 3, 1972 LINE TRAPSFOR POWER LINE Primary Examiner-Thomas J. Kozma CARRIER CURRENT SYSTEMSAttorney-A. T. Stratton, F. P. Lyle and Gordon H. [72] Inventor: Oral L.Riggins, Odon, Ind. Telfer [73] Assignee: Westinghouse ElectricCorporation, [57] ABSTRACT Plttsburgh A line trap is provided in anarrangement facilitating [22] Filed: Sept. 24, 1970 current balancebetween a plurality of layers as well as pp No: 74,993 providingmechanical stability. The line trap includes a coil of an electricalconductor with an end frame at each end that comprises a plurality ofbars extending 52 US. Cl. ..336/192, 336/84, 336/197, radially Outwardfrom a central The radial bars 336/207 are mechanically attached to thecoil structure and [51] Int Cl H0 27/08 Holf 15/10 also provide a pathfor electrical conduction from the layers of the coil to centrallylocated connector taps. [58] Field of Search ..336/ 197, 84, 207, 192,199 The n di 81 bars also permit terminating coil layers at 56 R f Cteddesired fractions of a turn to achieve current balance. 1 e erencesPreferably the layers of the coil have turns uniformly UNITED STATESPATENTS spaced from the axis with uniform spacing between adjacent turnsof all the layers. 1,747,507 2/1930 George ..336/207X 1,813,994 7/1931George ..336/207 X FOREIGN PATENTS OR APPLICATIONS 5 Claims, 5 DrawingFigures 756,250 4/1967 Canada ..336/207 my 7 I '7 7 7 Q IO l5 -I9 4o 2l4 S24 32 o o o 24 40 a ,so- 0 a 1 26 0 r. G 2

PATENIEnnma m2 3.696.315

SHEETIUFZ WITNESSES INVENTOR JZWM%W Orol L. Riggins PATENTEDucr 3 I972SHEET 2 BF 2 FIG.4.

LINE TRAPS FOR POWER LINE CARRIER CURRENT SYSTEMS BACKGROUND OF THEINVENTION inductive impedance in the carrier current system. The

line traps are connected directly to the transmission line and have tobe able to carry currents ranging from hundreds of amperes up to atleast a few thousand amperes. In designing and manufacturing a linetrap, it is important to consider size and weight factors for minimumcost as well as to provide an apparatus for the desired electricalfunction Without incurring problems because of the large mechanicalstresses that can be produced by such large currents.

To keep line trap structures in moderate size, it has been known that itis helpful to use a plurality of coil layers connected in parallel.Ordinarily, the prior art has been limited to coils of only twolayers-because of difficult problems in achieving current balancebetween layers of ,a coil having more than two layers. Current balanceis important because it provides the lowest power loss and lowestmechanical stresses. Severe stresses can result from current imbalancethat produces a temperature imbalance in the coil. The current magnitudein each layer depends on its impedance as well as the effect of theadjacent layers magnetic flux. Thus there has not been apparent astraightforward manner to achieve new inductance values while readilymaintaining current balance.

There has been a known design technique for line traps having coils ofthree layers in which the turns in successive layers are spread over thesame axial length, with fewer turns in the successively outward layers.This results in unequal spacing between turns in the various layersproducing difficult manufacturing problems to achieve current balance.

The prior art has also employed arrangements of two layers in the coilsin which the turns in both layers have the same uniform spacing. Such anarrangement has been satisfactory but has been limited to application inonly two layers because of difficulty in achieving current balance insuccessive layers. That is, it has not been considered a straightforwardprocedure to extend the arrangement conventionally used for two layersto coils with a larger number of layers.

SUMMARY OF THE INVENTION cal stresses.

Each end of the coil is secured to an end frame that comprises aplurality of bars extending radially outward from a central hub. Thebars are of conductive material and provide, in addition to mechanicalsupport, an electrical path from the various coil layers to connectortaps located proximate the center of the end frame. The plurality ofconductive bars, for example eight, pemrits connection to a particularlayer of turns at increments of a coil, such as one'eighth of a turn, asmay be found necessary to achieve proper current balance.

The turns in each of the coil layers are uniformly spaced from thecentral axis with uniform spacing between adjacent turns. The turns inthe outer layers are directly radially spaced from adjacent turns of thenext inner layer. The outer turns are generally (but not necessarily) offewer turns than the inner layers and are symmetrically arranged withrespect to the center of the innermost layer. The number of coil layersused may be up to six or more with adequate current balance.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view ofapparatus in accordance with one embodiment of the present invention;

FIG. 2 is an end elevation view of the apparatus of FIG. 1;

FIG. 3 is a partial sectional view of a coil that may be used in theapparatus of FIGS. 1 and 2;

FIG. 4 is a partial elevational view of a portion of the apparatus ofFIGS. 1 and 2; and

FIG. 5 is a partial perspective view of an interior portion of theapparatus of FIGS. 1 and 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the drawing, particularlyFIGS. 1, 2 and 3, the line trap comprises a cylindrical coil section 10with an end frame 12 at each end thereof. The coil section 10 comprisesa plurality of layers of turns 14 through 19 concentrically arrangedabout a center axis 20. In the example illustrated, six such layers areshown although the invention is not so limited. The layers 14 and 19 areelectrically in parallel. The coil conductor is a cable of sufficientsize to enable carrying the currents encountered in applications forline traps. It has in the past been necessary to use large cables foranother reason, that is to help minimize current unbalance between thevarious layers. In accordance with this invention, it is made practicalto use several smaller cables which permit the construction of the linetrap of smaller overall dimensions with less material therein.Commercial apparatus in accordance with the present invention has beenconstructed with cables having a diameter of 0.891 inch whereas priorline traps conventionally had cables of substantially larger size.

The coil layers 14 through 19 are supported in fixed position withuniform spacing between adjacent turns of a layer and between thevarious layers by axially extending bars 22 which may be of a cast orpremolded plastic material.

Each end frame 12 of the line trap (see FIG. 2) comprises a plurality ofconductive bars 24 extending radially outward from a hub 26 at the axialcenter of the frame. The radial bars 24 may be of cast or sheet aluminumand provide structural support as well as electrical continuity from thevarious coil layers 14-19 to terminals proximate to the hub 26. In thisembodiment there are eight radial bars 24 in each end frame 12 althoughthe number may obviously be varied. As shown in FIG. 4 as an example, asupport bracket 28 extends from a radial bar 24 around the end of one ofthe axially extending coil support bars 22 to unite the end frame 12 andthe coil structure 10. Also conductive connection is made from each ofthe several layers to one of the radial bars 24 at each end by aplate-like cable adapter member 29. The bracket 28 is a U- shaped memberrigidly joined to bar 24 and member 29. FIG. 4 also shows the end ofaxial bar 22 resting in a notch in bar 24 (the arrow shows the directionto the hub 26). In the example of FIG. 4 the bracket 28 joins the thirdand fourth coil layers 16 and 17 to the particular bar 24 shown. Otherones of the bars 24 will connect with coil layers 14, 15, 18 and 19either singly or in multiples. Some of the individual bars 24 will haveno electrical function and will merely support an end of a bar 22.

Around the periphery of the radial bars 24 extends a circular coronaring 30 which comprises arcuate sections 32 of conductive pipe, such asof aluminum, that are insulated from each other by insulative inserts 34such as of fiberglass to prevent circulating currents.

Terminal points 50 for external connection of the line trap are providedon the radial bars 24 towards the hub 26 with various radial positionsto permit ease in making the necessary connections. The terminal points50 are each a pattern of holes in the bars 24 for receiving a standardconnector of an external conductor.

A principal advantage of the present invention is the degree offlexibility permitted in thechoice of the exact length of each coillayer so as to achieve close current balance. It is here possible toconnect to the various coil layers at certain fractions of a turn whichcan have a pronounced effect and greatly facilitate achieving currentbalance. In the embodiment illustrated, eight positions are availablefor connection to the six coil layers. In other forms, greater numbersof bars 24 would permit even greater flexibility in this regard.

Another advantage of this invention principally result from a manner ofwinding the various coil layers so that they are readily assembled. FIG.3 illustrates the coil arrangement wherein the various coil layers 14-19each have uniform spacing between turns. For the example previouslyreferred to of 600 MCM cable a spacing between layers of approximately1.41 inches center to center has been used. The basic arrangement ofturns is simply that the first inner layer 14 having the greatest numberof turns (because of the smallest diameter of the turns) has disposedaround it the succesive layers l9 of (usually) lesser turns which aresymmetrically disposed about the axial center of the first layer. Thechange in axial length of the coil layers while retaining uniformspacing between turns of the layer permits ease of assembly and permitsa consistent coil fabrication technique to be applied essentiallyregardless of the size of the line trap.

The exact number of turns in each layer is necessarily determined atleast in part empirically. It has been found in the practice of thisinvention that it is not always desirable that outer layers have fewerturns. In an example of coils of six layers that have been made of 0.891inch diameter cable on 1.41 in. centers, outside overall coil diameterabout 6 feet, the numbers of turns in each layer were:

lst layer I4) 40 turns 2nd layer I5) 34% turns 3rd layer (16) 30% turns4th layer 17) 29% turns 5th layer I8) 28% turns 6th layer I9) 28% turnsThe increase in the sixth layer over the fifth is a result of fluxintensity in the combination. This line trap was rated at 3,000 amperesand 1.00 milli-henries and has a current that is balanced within 1 1percent. For different current ratings, the number of coil layers needmerely be changed (500 arnperes per layer using the cable referred to).For different inductance ratings merely the length (number of turns inthe various layers) need be changed. Thus a consistent assemblyprocedure is provided.

Referring to FIG. 5, the two end frames 12 are held to each other withinternal support members 36 on rigid V-shaped brackets 38. Element 36 isa sandwich of three fiberglass sheets, the internal one of which has Vnotches to receive the brackets 38 and the outer ones overlap the endsof the brackets and are securely joined. Torsional forces that areinduced at each end of the line trap by the current passing through thecoil are transferred to the other end and are thereby cancelled. Plates40 that are joined to the radial bars 24 provide anchor points 42 forthe strain members 36.

I claim:

1. A line trap to provide inductance for a power line carrier currentsystem comprising: a coil of an electrical conductor, said coil havingat least first and second concentric, electrically parallel, layers ofturns about a central axis, said turns in each of said layers beinguniformly spaced from said axis with uniform spacing between adjacentturns, said second layer being spaced outside said first layer andcomprising a number of turns directly radially spaced from turns of saidfirst layer, and end frame at each end of said coil supporting said coiland including means to terminate said layers at fractions of a full turnto achieve current balance between said layers, and a plurality ofaxially extending bars joined at their ends to said end frames andarranged in a generally cylindrical configuration, said axial barshaving said turns of said layers extending therethrough to secure theuniform positioning of said turns.

2. The subject matter of claim I further comprising: said at least firstand second layers of turns including a third layer of turns directlyradially spaced from turns of said first and second layers, said secondand third layers being each disposed symmetrically about the axialcenter of said first layer.

3. A line trap to provide inductance for a power line carrier currentsystem comprising: a coil of an electrical conductor in a plurality ofturns about a central axis; and end frame at each end of said coilcomprising a plurality of bars extending radially outward from a centralhub, said bars supporting said coil and also electrically connecting tosaid coil; said coil having at least first and second concentric layersof turns about a central axis, said turns in each of said layers beinguniformly spaced from said axis with uniform spacing between adjacentturns, said second layer being outside said first layer of turns andcomprising a number of between said end frames extends between platemembers of said two end frames.

5. The subject matter of claim 3 wherein: said radially extending barssupport terminals for external electrical connection of said line trap;said coil layers each being terminated at a selected one of saidradially extending bars to provide coil layer lengths of integral turnsand fractions of a turn that result in current balance between saidlayers.

1. A line trap to provide inductance for a power line carrier currentsystem comprising: a coil of an electrical conductor, said coil havingat least first and second concentric, electrically parallel, layers ofturns about a central axis, said turns in each of said layers beinguniformly spaced from said axis with uniform spacing between adjacentturns, said second layer being spaced outside said first layer andcomprising a number of turns directly radially spaced from turns of saidfirst layer, and end frame at each end of said coil supporting said coiland including means to terminate said layers at fractions of a full turnto achieve current balance between said layers, and a plurality ofaxially extending bars joined at their ends to said end frames andarranged in a generally cylindrical configuration, said axial barshaving said turns of said layers extending therethrough to secure theuniform positioning of said turns.
 2. The subject matter of claim 1further comprising: said at least first and second layers of turnsincluding a third layer of turns directly radially spaced from turns ofsaid first and second layers, said second and third layers being eachdisposed symmetrically about the axial center of said first layer.
 3. Aline trap to provide inductance for a power line carrier current systemcomprising: a coil of an electrical conductor in a plurality of turnsabout a central axis; and end frame at each end of said coil comprisinga plurality of bars extending radially outward from a central hub, saidbars supporting said coil and also electrically connecting to said coil;said coil having at least first and second concentric layers of turnsabout a central axis, said turns in each of said layers being uniformlyspaced from said axis with uniform spacing between adjacent turns, saidsecond layer being outside said first layer of turns and comprising anumber of turns directly radially spaced from turns of said first layer;and a plurality of axially extending bars joined at their ends to saidend frames and arranged in a generally cylindrical configuration; saidaxial bars having said turns of said layers extending therethrough tosecure the uniform positioning of said turns.
 4. The subject matter ofclaim 3 wherein: each of said end frames comprises a plurality of platemembers, each said plate member joined to an adjacent pair of said bars;and a means for transmitting torsional forces between said end framesextends between plate members of said two end frames.
 5. The subjectmatter of claim 3 wherein: said radially extending bars supportterminals for external electrical connection of said line trap; saidcoil layers each being terminated at a selected one of said radiallyextending bars to provide coil layer lengths of integral turns andfractions of a turn that result in current balance between said layers.